No abstract

The analysis of the behavior of fuel pins irradiated in the same Rapsodie subassembly, shows that titanium has a marked beneficial effect on the swelling resistance of cold-worked Type 316 stainless steel in a wide temperature range. This effect is particularly visible at high temperature since cold-worked Type 316 titanium does not swell above 550°C up to a dose of 100 French displacements per atom (dpaF)(∼74 dpa NRT). The results obtained on samples irradiated in a Rapsodie experimental rig give us confirmation of the good behavior of cold-worked Type 316 titanium stainless steel that swells less and at lower temperature than other steels of the Type 316 series such as solution-annealed Type 316 titanium or aged solution-annealed Type 316 titanium. The swelling differences between some of these materials can be associated with different microstructures that are also very different from the ones obtained on the unirradiated steels aged for the same time and temperature conditions.

In this work, we describe the precipitation behavior of cold-worked titanium-stabilized Type 316 stainless steel irradiated with neutrons in the temperature range of 464 to 596°C. The samples were cut from a Rapsodie fuel pin cladding and were examined by transmission electron microscopy and energy dispersive X-ray micro-analysis. The microstructure is characterized by the precipitation of G and eta phases in the temperature range of 464 to 521°C, and TiC and Laves phases above 590°C. The results also emphasize the important effect of dose rate on the precipitation, and particularly on the chemical composition of the Laves phases. The most striking feature is the appearance above 546°C of thin platelets whose diffraction characteristics are coherent with the hexagonal Ni3Ti phase. The formation of a high density of these planar may partly explain the low swelling of cold-worked titanium-stabilized Type 316 stainless steel above 540°C.